package foundation.area_of_a_circle;

import java.util.Scanner;

/**
 * 给定圆的半径r，求圆的面积。
 */
public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int r = sc.nextInt();
        System.out.printf("%.7f", Math.PI * Math.pow(r, 2));
    }
}
